Building tires in the foregoing manner is not exceedingly difficult, however, if not done with great care and upon accurate equipment, premature problems may develop which can lead to unsatisfactory operation of the resultant tire or possibly failure during use. With particular respect to second stage operations, accurate belt (tread ply) placement in relation to the centerline of the tire carcass is of the utmost importance in order to eliminate undue wear and/or defects in the tire. One of these defects, known as conicity, occurs when the belt ply is not applied directly over the centerline of the carcass and causes the vehicle upon which the tire is mounted to tend to steer in a circle. As a consequence, the car pulls to one direction and excess adjustment in wheel alignment is necessary to correct the condition. Lateral force variation can also occur if the belt ply is applied on the carcass crooked and will cause the tire to meander left and right during rotation. In addition, premature wear on the tire and undue flexing of the belt can also occur which can give rise to its failure, particularly in steel reinforced belts.
The misplacement of carcass components such as belts (tread plies) can be attributed to carelessness on the part of the operator, faulty equipment and other reasons. Existing equipment has most commonly been made adjustable so that the tire builder can construct more than one size of tire on a given machine. In order to accommodate a variety of component sizes for different tires, the flexibility designed into the machine is often at the expense of rigidity and stability thereof, directly affecting the degree of accuracy with which even the most careful operator can build a tire. Existing tire building equipment has not successfully eliminated the possibility of misadjustment by the operator or maladjustment occasioned by wear of the equipment.
Exemplary apparatus of the foregoing type is depicted in British Pat. No. 1,375,555. This patent as well as U.S. Pat. No. 2,814,330 and 2,814,331 also disclose centering guides which are provided for the accurate placement of belts; however, these are too low to be totally effective in instances where the belts are hurriedly applied or are improperly dimensioned.
A building drum which does not require simultaneous movement of both sides toward the center in order to impart a toroidal shape to the carcass, is described in U.S. Pat. No. 3,929,540. This patent does not provide a satisfactory means by which the belts can be accurately applied to the carcass and thus does not represent a substantial improvement over the prior art.
The British apparatus further typifies the prior art in that the expansion of the tire carcass from cylindrical to toroidal shape is occasioned by simultaneously moving the ends of the drum toward the center. Although such a mechanism is effective for expanding the carcass, eventual mechanical play or wear will lead to maladjustment and if uncorrected, will result in the inaccurate building of the tire or similar article.